The air filters are made of specialty blended self-extinguishing, polyester graduated media which far exceed UL Standard 900 Class 2 for fire resistance. The material is heat sealed into specific sizes and shapes tailored to fit each generator style. Due to their unique design, the filters deal against the motor generators, which prevents carbon dust leakage and bypass. These filters are designed to provide long life and low pressure drop. (This process is unique and patented.) In some cases, holding frames are used to mount the filters described above. These frames are made from 26 gauge galvanized steel or aluminum, creating a 2 or 3 sided 7/8" slide-in or snap-in channel where filters are inserted. This system is successful and is used extensively in the HVAC industry. The holding frames are attached to the motor generator using 3M® 2-sided adhesive industrial tape which bonds on contact and cures 100% in 72 hours. Other filter designs are supported and do not require holding frames. They conform to the contour of the generators and often secure to the generator with Velcro®.